davmailservice64.exe is just the Winrun4J binary with embedded ini file

Thus if you have to customize it the easiest approach is to get original ini file from:
https://github.com/mguessan/davmail/blob/master/src/winrun4j/davmailservice64.ini
, copy it to davmailservice64.exe directory and adjust it to your requirements.

If I remember correctly you don't even need to update ini inside exe file

Note: sorry for the late answer